For example, if you found that the mean height of male Biology majors was significantly larger than that of female Biology majors, you might report this result (in blue) and your statistical conclusion (shown in red) as follows:
We observed associations between daily PM2.5 concentrations and pediatric ED visits for asthma or wheeze and for upper respiratory infections. The OR estimate for bronchitis was similar in magnitude to the ORs for asthma or wheeze and upper respiratory tract infections, although the confidence interval included the null. We saw little evidence for the other outcomes examined. Differences in the association estimates across levels of urbanicity were not statistically significant.
Longitudinal studies show that there is a high correlation between aggression and violence in early and middle childhood with violence in adolescence and into adulthood (Astor, 1995).
We also conducted sensitivity analyses to examine the impact of missing data on OR estimates. In the two most extreme cases, we either a) only analyzed ZIP codes that had complete 1-km grid PM2.5 estimates or b) analyzed as many data as possible (i.e., so long as a ZIP code had at least one 1-km grid PM2.5 estimate it was included in the analysis). We also examined results for a range of missing data scenarios between these two extremes. These sensitivity analyses informed our decision to exclude a ZIP code when > 70% of the grid estimates were missing on a given day.
In the mouse behavior paper, for example, you would begin the Introduction at the level of mating behavior in general, then quickly focus to mouse mating behaviors and then hormonal regulation of behavior.
We did not observe statistically significant associations between short-term PM2.5 exposure and the other outcomes examined. Otitis media is a common pediatric disease that has been associated with environmental tobacco smoke and indoor wood burning (; ). A small number of studies have been conducted to investigate associations between outdoor air pollutants and otitis media; the study most similar to ours—a case-crossover analysis of 14,527 ED visits for otitis media in Edmonton, Canada—found associations for carbon monoxide and nitrogen dioxide but not for PM2.5 (). Our study, which had the advantage of having many more ED visits for otitis media (n = 237,833 visits) but which was exclusively focused on PM2.5, similarly found little evidence of this association. Results of studies on the association between chronic PM2.5 exposure during early life and otitis media have been inconsistent (, ). Associations of short-term changes in PM2.5 concentration with pediatric pneumonia and bronchitis, two other outcomes that we investigated in our study, have been previously reported (; ), although the associations in our study were not statistically significant.
Lag 0 associations stratified by level of urbanicity are presented in (for numerical results, see Table S1). These analyses did not suggest large differences in the associations of outdoor PM2.5 concentrations with ED visits by level of urbanicity. For the three most common outcomes (asthma/wheeze, otitis media, and upper respiratory infections) the association estimates were similar across urbanicity levels (p-values from the generalized Wald test for “H0: the three stratum-specific ORs are equal,” the null hypothesis we were testing, were 0.85, 0.99, and 0.69, respectively). In contrast, the ORs for the less common outcomes tended to be negative in urban areas and positive in less urban areas (p-value for differences across strata of 0.12–0.15), although estimates were imprecise. The lag 1 results similarly did not suggest large differences in associations by level of urbanicity (results not shown).
We observed that short-term changes in lag 0 and lag 1 PM2.5 concentrations were associated with ED visits for asthma or wheeze and with ED visits for upper respiratory infections. Broadly, these findings are consistent with previous literature that also shows associations between PM2.5 and pediatric respiratory disease (). We found little evidence of effect modification by level of urbanicity, even though the composition of PM2.5 differs in urban and rural areas (). For example, motor vehicle engine combustion particles comprise a larger proportion of PM2.5 in urban areas, whereas nonmetropolitan areas tend to have proportionately greater contributions from biogenic, forest fire, and ammonia emissions (). A limitation of our study is that particle composition was not characterized. Furthermore, although sample size for these two outcomes was large, we might not have detected effect modification if it was of small magnitude.
For example, controls, treatments, what variable(s) were measured, how many samples were collected, replication, the final form of the data, etc.);
Studies have also shown that a high frequency of violent acts in early childhood is significantly related to the severity of violence and criminal behavior in adolescence and adulthood (Astor, 1995).
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The Abstract helps readers decide whether they want to read the rest of the paper, or it may be the only part they can obtain via electronic literature searches or in published abstracts.